Strong magnets include electromagnets and permanent magnets. An electromagnet capable of producing a large magnetic field is cumbersome and requires a very large power supply. Permanent magnets exist of relatively compact size that are capable of producing large magnetic fields. However, permanent magnets cannot be turned off and since their polarity is not rapidly switching, they saturate surrounding permeable material and their emitted field cannot be attenuated. Consequently, permanent magnets are difficult to shield and those that produce large magnetic fields are difficult to handle and store in many settings for which such a magnet might otherwise be useful.
For example, the use of magnetically responsive particles to target drug(s) and/or therapeutic agent(s), device(s) or diagnostic(s) to specific sites through the selective application of a magnetic field, and to achieve prolonged release of high, localized concentrations of drug and/or diagnostic agent by retention of magnetic particles in the region of interest is possible. The externally applied magnetic field produced by a permanent magnet can be used to control the migration and retention of such particles at target sites. However, handling and storage of such a magnet in a clinical setting would be challenging.
The present invention relates to an apparatus comprising a keeper-shield and a permanent magnet mounted within the keeper-shield. The apparatus renders the magnet easier to store and handle in a variety of settings and for many applications. The details of the invention are set forth in the accompanying drawings and the description below. Other features, objects and advantages of the invention will be apparent from the description and drawings, and from the claims.